Recovery of uranium from HCl digested phosphate rock solution

ABSTRACT

Uranium is recovered from a solution containing phosphoric acid, uranium in the hexavalent state and a chloride salt from the group consisting of alkali metal chloride, alkaline earth metal chloride, ammonium chloride and mixtures thereof, such as a solution obtained by hydrochloride acid digestion of phosphate rock. The phosphoric acid is extracted from the solution before the uranium is recovered from the remaining constituents thereof. Extraction degradation and emulsification of the organic layer previously employed in organic solvent extraction methods are eliminated, and the uranium is recovered at low cost and in a highly efficient manner.

United States Patent [1 1 Wamser 1 Apr. 29, 1975 1 RECOVERY OF URANIUMFROM HCl DIGESTED PHOSPHATE ROCK SOLUTION [75] Inventor: Christian A.Wamser, Camillus,

[21] Appl. No.: 311,012

[52] US. Cl. 423/7; 423/8; 423/15; 423/18 [51] Int. Cl C(llg 43/02 [58]Field of Search 423/6, 7, 8, 9, 10, 15, 423/18, 20, 260, 319, 321, 253;23/312 P, 312 ME [561 References Cited UNITED STATES PATENTS 2,770,52011/1956 Long ct a1 .1 423/7 2,797,143 6/1957 Arcndale et a1. 423/182.859.092 11/1958 Bailes ct a1. 423/253 X 2,926,992 3/1960 Stcdman l423/18 3.072461 1/1963 Long et a1 423/319 3,174,821 3/1965 Opratko et a1423/15 3,433,592 3/1969 Baniel et a1. 23/312 P 3,479,139 11/1969 Koerncr23/312 P 3,595,613 7/1971 Klingclhoefer 23/312 P 3,737,513 6/1973Wiewiorowski et al. 423/8 Primary Examiner-Stephen J. Lechert, Jr.

Assistant Examiner-E. A. Miller Attorney, Agent, or Firm-Gerard P.Rooney; Ernest D. Buff [57] ABSTRACT Uranium is recovered from asolution containing phosphoric acid, uranium in the hexavalent state anda chloride salt from the group consisting of alkali metal chloride,alkaline earth metal chloride, ammonium chloride and mixtures thereof,such as a solution obtained by hydrochloride acid. digestion ofphosphate rock. The phosphoric acid is extracted from the solu tionbefore the uranium is recovered from the remaining constituents thereof.Extraction degradation and emulsification of the organic layerpreviously employed in organic solvent extraction methods areeliminated, and the uranium is recovered at low cost and in a highlyefficient manner.

11 Claims, N0 Drawings RECOVERY OF URANIUM FROM HCl DIGESTED PHOSPHATEROCK SOLUTION BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to the recovery of uranium from a phosphoric acidcontaining solution, and more particularly to a process for extractingphosphoric acid from the solution before the uranium is recovered.

2. Description of the Prior Art The demand for uranium is continuouslyincreasing, but relatively few extensive high grade uranium depositshave been found. Fortunately, many phosphate rocks contain small amountsof recoverable uranium. The tonnage of phosphate rock consumed duringmanufacture of phosphoric acid is considerable. Hence, it is apparentthat a substantial amount of uranium could be made available therefromby provision of an efficient, economical method of recovery. Unlessuranium is recovered during manufacture of phosphoric acid, it has beenestimated that more than two thousand tons of uranium from this sourcewill be lost each year. The need for such a method of recovery cannot beoverstated, since future growth 'of electric power generation by nuclearmeans depends to a large extent on an economical source of uranium fuel.

The methods which have enjoyed, perhaps, the widest use in recoveringuranium from phosphate rock during manufacture of phosphoric acid are ofthe types disclosed in U.S. Pat. Nos. 2,761,758, 2,859,092 and2,866,680. In each of those methods uranium is recovered directly fromthe product acid, but to date considerable problems inherent in the useof such methods have not been solved. The coprecipitation method of US.Pat. No. 2,761,758 is time consuming for relatively large volumes ofphosphoric acid, is multistep, and requires recycle procedures. Organicextractants, such as the ethyl phosphates employed in the solventextraction methods of US. Pat. Nos. 2,859,092 and 2,866,680, tend todegrade so as to require constant addition of make-up amounts. Moreover,emulsification of the organic layer in the aqueous phase of such solventextraction methods necessitates additional stripping procedures toprevent solvent loss.

Ion exchange, normally a preferred separation method when applicable,has been found not useful for methods of the types described above. Thehexavalent uranium present in the phosphoric acid forms an anioniccomplex which is an improper target for cation exchange.Phosphorus-containing ions present in the product acid are readilyadsorbed by anion exchange resins, with the result that the selectivityof such resins for uranium complexes is substantially decreased. For theabove reasons, methods of the type described have generally resulted inlower efficiencies and higher costs for recovering uranium than havebeen considered commercially acceptable.

SUMMARY OF THE INVENTION The present invention provides an economicaland efficient method for recovering uranium present in a solutioncontaining phosphoric acid, uranium in the hexavalent state and achloride salt from the group contion, the phosphoric acid is extractedbefore the uranium is recovered from the :solution. This is accomplishedby contacting the solution with a reductant capable of converting theuranium from a hexavalent to a tetravalent state. After the solution hasbeen reduced in this manner, it is brought into contact with an organicextractant capable of separating the phosphoric acid therefrom.Thereafter, the uranium is recovered from the remaining constituents ofthe solution.

It has been found that significant advantages result from extracting thephosphoric acid from the solution and then recovering the uranium fromthe remaining constituents thereof. The numerous steps and recycleprocedures required by coprecipitation methods are avoided. Problemssuch as extractant degradation and emulsification of the organic layerpreviously employed in solvent extractant methods are eliminated. Uponextraction of the phosphoric acid, the uranium is readily converted fromthe tetravalent to the hexavalent state and adsorbed from the solutionin a highly efficient manner by contacting the remaining constituentsthereof with an ion exchange resin. Adsorption of uranium issubstantially complete, i.e. at least about percent by weight of theuranium is adsorbed. Moreover, the uranium is adsorbed by the resin as acomplex chloride ion, so that the adsorbing column can be economicallyregenerated with water. For the above reasons, recovery of the uraniumresults in higher efficiencies and lower costs than those incurred byoperations wherein the solution from which the uranium is recoveredcontains phosphoric acid.

The invention will be more fully understood and further advantages willbecome apparent when reference is made to the following detaileddescription of the preferred embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Most phosphoricacid-containing solutions, including those obtained during variousstages of superphosphate and industrial phosphoric acid manufacture asbyproducts and as intermediate products, contain uranium. As aconsequence, the present invention will function with most types ofphosphoric acid-containing solutions. For illustrative purposes, theinvention is described in connection with a solution obtained byhydrochloric acid digestion of phosphate rock. However, solutionsdiffering very considerably in composition from the latter solutioneither in relative concentrations or in the types of ions present canalso be satisfactorily processed by the invention. Moreover, it iscontemplated that phosphate may be added to acidic uranium solutions andthe uranium recovered by the process of the invention. In each of thesephosphoric acidcontaining solutions, the necessity for recoveringuranium in an economical and efficient manner is readily apparent.

The starting material may be any solution containing phosphoric acid,uranium in the hexavalent state and chloride salt from the groupconsisting of alkali metal chloride, alkaline earth metal chloride,ammonium chloride and mixtures thereof. Of course, the starting materialcan contain uranium in each of the hexavalent and tetravalent states. Acommon starting material is the solution obtained by hydrochloric aciddigestion of phosphate rock, during the conversion of the rock intofertilizer. The method of obtaining such solution is well known to thoseskilled in the art. Generally, an aqueous slurry of such rock isintroduced into an acidulating vessel wherein it is treated withhydrochloric acid to form a solution containing phosphoric acid, uraniumand chloride salts, principally as calcium chloride. The solution isthen transferred to a reducing vessel wherein it is brought into contactwith a reductant capable of converting the uranium from the hexavalentto the tetravalent state. After the solution has been reduced in thismanner, it is transferred to an extracting vessel wherein it is causedto contact an organic extractant capable of removing the phosphoric acidtherefrom. It was discovered that uranium in the tetravalent state isnot separated from the solution during extraction of the phosphoricacid, but instead remains in the resulting solution, comprising anaqueous brine phase, from which it is recovered in a highly efficientmanner, as by passing the solution through an anion exchange resin.

The concentration of the uranium present in the starting solution canvary considerably, as in the order of from about 10-2000 parts by weightof uranium per million parts by weight of solution, and preferably fromabout l-l000 parts by weight of uranium per million parts of solution.Uranium in the tetravalent state tends to become insoluble atconcentrations higher than about 2000 parts by weight uranium permillion parts by weight of solution, with the result that a tetravalenturanium dihydrogen phosphate precipitate is formed which interferes withthe extraction of the phosphoric acid and leads to uranium lossesthrough deposition of solids in the extraction equipment. Theconcentration of phosphoric acid present in the starting solutiongenerally ranges from about 1-50 weight percent of the solution, andpreferably from about 5-30 weight percent thereof. Concentrations ofphosphoric acid below about one percent by weight of the solution tendto result in precipitation of tetravalent uranium phosphate. Atconcentrations of the phosphoric acid above about 50 percent by weightof the solution, the solubility of the chloride salt decreases rapidlyand extraction of the phosphoric acid is reduced.

In addition to promoting extraction of the phosphoric acid, the chloridesalt forms a complex with uranium which is retained by the resin in theion exchange column, whereby the column can be economically regeneratedwith water. The required amount of chloride salt will, of course, varydepending upon the type of salt present and such considerations will beunderstood by those skilled in the art. Generally, solutions obtained byhydrochloric acid digestion of phosphate rock already contain asufficient quantity of chloride salts, principally as calcium chloride.As a result no chloride salt has to be added to such solutions. Duringextraction, distribution of phosphoric acid into the organic phaseincreases directly with the chloride salt concentration. At chloridesalt concentrations above about 30 percent by weight of the solution,the chloride salt tends to enter the organic phase. Calcium chlorideconcentrations below about 5 percent by weight of the solution tend tohinder separation of the tetravalent uranium and the phosphoric acidduring the extraction step. Accordingly, for most effective separationof the tetravalent uranium and phosphoric acid during extraction of thelatter, the calcium chloride concentration should range from about 5-30percent by weight of the solution.

The reductant employed to convert the uranium from a hexavalent to atetravalent state should not hinder extraction of phosphoric acid byadversely affecting either the phosphoric acid or the organic solvent.Moreover, such reductant should be oxidized to a form whereby thereductant (1) does not interfere with recovery of uranium from the brinephase in which the uranium is retained during extraction of thephosphoric acid, or (2) is readily separable from the brine phase.Reductants which have been found particularly effective for the methodof the present invention include elementary iron, elementary aluminum,hydrogen sulfide, sodium hydrosulfite and formaldehyde-sodiumsulfoxylate. The preferred reductant is hydrogen sulfide since itsoxidation product, elementary sulfur, is readily separated from thesolution prior to extraction of the phosphoric acid therefrom.

Reduction of the uranium from the hexavalent to the tetravalent statecan be conveniently carried out at temperatures ranging from about 10C.to the boiling point of the solution and preferably from about 40C. toC. Generally, the uranium is associated with relatively largeproportions of iron, thus the Fe/U weight ratio in a HCl-phosphate rockdigest liquor is approximately 50. Moreover, all the iron must bereduced to the divalent state before any U can be reduced to thetetravalent state. As a result, the amount of reductant required iscontrolled by the iron rather than the uranium. Since the reduction stepis relatively slow when weak reductants are employed, a catalyst, suchas a soluble copper salt (e.g. copper sulfate or chloride), may be addedto increase the rate of the reduction reaction. The copper catalyst hasbeen found to be effective when added in an amount ranging from about0.005 to 0.05 mole copper per mole of hexavalent uranium, and preferablyabout 0.01 mole copper per mole of hexavalent uranium.

The extractant used to separate phosphoric acid from the solution mustbe phosphoric acid-miscible and brine-immiscible. Moreover, theextractant must not separate the tetravalent uranium from the solution.Good results have been obtained using organic extractants such asbutanols (e.g. Z-methyl-l-propanol), pentanols (e.g.3-methyl-l-butanol), trialkylphosphates having alkyl groups containingfrom 2 to 8 carbon atoms (e.g. tri-n-butylphosphate), and N,N-disubstituted amides which are derived from monocarboxylic acids having1 to 3 carbon atoms (e.g. N,N- dibutyl acetamide), as well as frommixtures of the foregoing extractants individually or in combinationwith kerosene or other hydrocarbons. Best results are obtained usingbutanols and pentanols diluted with kerosene or heptane. The amount ofextractant used may vary depending on the concentration of phosphoricacid in the solution as well as the type of extractant. Generally, theamount of extractant used ranges from about 5 to 20 parts by weight perpart of the phosphoric acid, and preferably from about 10 to 15 partsper part thereof.

As indicated, after the phosphoric acid has been extracted from thesolution, the uranium can be efficiently and economically recovered fromthe remaining solution comprising an aqueous brine phase. The brinesolution is transferred to an oxidizing vessel wherein the constituentsthereof are brought into contact with an oxidant capable of convertingthe uranium from the tetravalent to the hexavalent state. When oxidationof the uranium is substantially complete, the brine solution is directedthrough an ion exchange column wherein it contacts an anion exchangeresin such as Dowex-l (a registered trademark of the Dow ChemicalCompany for an anion exchange resin made from a styrene-divinylbenzenecopolymer), Amberlite IRA- 400 (a registered trademark of Rohm and HaasCompany for an anion exchange resin comprising an insoluble cross-linkedpolymer), Permutit S (a registered trademark of Permutit Company for abasic anion exchange resin), or the like. Due to the presence of thechloride salt, the uranium tends to form anionic uranyl chloro-complexeswhich, upon contact with the resin, are substantially adsorbed. Theadsorbed uranyl chloro-complexes are removed from the column by means ofa solvent and uranium is then recovered from the resulting solution in amanner hereinafter described.

The oxidant which can be used to convert the uranium from thetetravalent to the hexavalent state include any oxidant which does notprevent or interfere substantially with the separation of uranium by theanion exchange resin. As discussed hereinafter, the amount of oxidantused should be no greater than that sufficient to convert thetetravalent uranium to the hexavalent state. Typical oxidants suitablefor use with the present invention include soluble trivalent iron salts(e.g. ferric chloride), sodium chlorate, sodium hypochlorite, sodiumchlorite and elementary chlorine. Elementary chlorine and sodiumchlorate are inexpensive, easily handled and form reduction productswhich do not interfere with the separation of uranium by the anionexchange resin. For this reason, the latter oxi dants are preferred.

The oxidation step can be carried out at atmospheric pressure and attemperatures ranging from about C. to the boiling point of the solution,and preferably from about 40C. to 100C. At temperatures lower than about10C., the chloride salt commences to precipitate from the solution andthe oxidation rate is retarded, thereby inconveniently prolonging theoxidation step.

The efficiency of the anion exchange resin depends on the chloride ionconcentration of the solution. Good results have been obtained with 310molar chloride ion solutions. The best results are obtained with 4-9molar chloride ion solutions.

Generally, the starting solution contains a trivalent iron salt presentin an amount ranging from about 1000 parts by weight of salt per millionparts by weight of so lution. During reduction of the uranium from thehexavalent to the tetravalent state, the trivalent iron is reduced tothe divalent state, and consequently, remains in the aqueous phase ofthe solution during extraction of the phosphoric acid therefrom. Toprevent oxidation of this iron to a trivalent state and coadsorptionthereof with the uranium as FeClfduring passage of the aqueous phase(brine solution) through the adsorbing column, the amount of oxidantused to convert the uranium from tetravalent to the hexavalent statemust be Carefully controlled. For this reason, the quantity of oxidantemployed should be no greater than that sufficient to convert thetetravalent uranium to the hexavaof sulfur dioxide in the solution doesnot reduce the uranium therein to a tetravalent state.

The uranium can, alternatively, be recovered from the brine solution byseparating the solution into a plurality of portions. A first portion ofthe solution is brought into contact with an oxidant of the typedescribed, the oxidant being present in sufficient quantity that each ofthe uranium and the iron contained therein become fully oxidized. Thusoxidized, the first portion is combined with a second portion-of thesolution in an amount sufficient to selectively oxidize substantiallyall of the uranium of the second portion from the tetravalent to thehexavalent state. By appropriate apportionment of the first and secondportions of the solution according to the formula 2Fe (III) U (IV) ZFe(II) U (VI) a resultant stream is produced having its uranium and ironconstituents in the form best suited for the adsorption step.

Uranium adsorbed by the ion exchange resin can be removed therefrom bywashing the resin with a solvent such as water or dilute hydrochloricacid. During the washing step the hexavalent uranium is dissolved by andenters the resulting solution in the form of uranyl chloride (UO CI Onemethod of recovering uranium from the solution comprises the steps ofneutralizing the solution with limestone to a pH of about 4, removingtrace impurities such as iron from the solution, as by filtering,introducing a sufficient quantity of ammonia to cause precipitation ofhexavalent uranium in the form of the compound ammonium diuranate (NH UO separating such compound from the solution, as by filtering, washingthe compound and calcining it to produce uranium trioxide (U0 Anothermethod of removing uranium from the solution comprises the steps ofevaporating the solution so as to bring the uranium concentrationthereof to at least about one percent by weight of the solution,contacting the solution with a sufficient amount of a reductant, such.as a hydroxylamine salt (e.g. hydroxylamine hydrochloride, hydroxylaminesulfate (NH OH'H SO to reduce the uranium therein from a hexavalent toa'tetravalent state, contacting the reduced solution with a sufficientamount of hydrogen fluoride (HF) and ammonium fluoride (NH F) toprecipitate uranium from the solution in the form of crystallineammonium uranous pentafluoride (NH UF and separating (as by filtering),washing and calcining the precipitate to form uranium tetrafluoride (UFThe above-described process for recovering the uranium in a desirableform (UFQ) is described in detail in U.S. Pat. No. 3,681,035, assignedto Allied Chemical Corporation.

In a specific embodiment of the present invention, a solution obtainedfrom hydrochloric acid digestion of phosphate rock was found to containfrom about 5-15 percent by weight phosphoric acid (H PO 20-30 percent byweight calcium chloride (CaCl l-Z percent by weight hydrochloric acid(HCl), 0.3 to 1.5% by weight ferric chloride (FeCl and 50200 parts byweight uranium per million parts by weight of solution. The solution wastreated at C. with a sufficient quantity of hydrogen sulfide to reducesubstantially all of the iron and uranium present therein to thedivalent and tetravalent states, respectively. An extractant composed ofa mixture of pentanols and kerosene was then introduced into thesolution, whereby 99.8 percent by weight of phosphoric acid wasextracted therefrom. The remaining constituents of the solution,comprising an aqueous uranium-containing brine phase were then separatedinto two portions. A first portion was fully oxidized upon contact withsodium chlorate (NaClO Thereafter, a second portion of the brine phasewas combined with a sufficient amount of the first portion thereof tooxidize substantially all of the tetravalent uranium in the secondportion from the tetravalent to the hexavalent state and tosimultaneously reduce an equivalent amount of the trivalent iron in thefirst portion to the divalent state. With the iron and uraniumconstituents of the resultant solution in the form best suited foradsorption, the solution was directed through an ion exchange columnwherein it was brought into contact with an anion exchange resin.Uranium adsorbed onto the resin was'then removed therefrom by washingthe column with dilute hydrochloric acid. The slightly acidic solutionwhich resulted was then treated with hydroxylamine sulfate (NI-I OH) 'HSO to reduce the uranium to the tetravalent state. Hydrogen fluoride andammonium fluoride were then introduced into the solution, whereby theuranium was separated from the solution in the form of ammonium uranouspentafluoride. The ammonium uranous pentafluoride precipitate was washedand then calcined at 350C. to produce uranium tetrafluoride.

The method described hereinabove can, of course, be modified in numerousways without departing from the invention. The extractant can berecycled after separation of phosphoric acid from the solution.Moreover, the ammonium fluoride removed from the precipitated ammoniumuranous pentafluoride by calcination can be recycled for use in formingthe ammonium uranous pentafluoride precipitate. Such modifications areintended to fall within the scope of the present invention. It is,accordingly, intended that all matter disclosed in connection with theforegoing method should be interpreted as illustrative and not in alimiting sense.

The following examples, in which parts and percentages are by weight,are presented to provide a more complete understanding of the invention.The specific techniques, conditions, materials, proportions and reporteddata set forth to illustrate the principles and practice of theinvention are exemplary and should not be construed as. limiting thescope of the invention.

EXAMPLE 1 A reaction vessel equipped with a mechanical stirrer wascharged at atmospheric pressure with an aqueous slurry of phosphaterock, hydrochloric acid and sodium chloride. The resultant startingsolution contained 25 percent calcium chloride, 13.1 percent phosphoricacid, 1.8 percent hydrochloric acid and 66 parts uranium (essentially inthe hexavalent form) per million parts of solution. These constituentswere heated with vigorous stirring to a temperature of 80C. The stirringwas continued, 0.55 gram of sodium hydrosulfite was added to thesolution and the temperature of the solution was maintained at 80C. forminutes, during which time substantially all of the uranium was reducedfrom the hexavalent to the tetravalent state.

The reduced solution was divided into ten one-liter portions. Anextractant was prepared by saturating a mixture of 80 percent isobutanoland percent nheptane with water at 50C. Substantially all of thephosphoric acid was extracted from the solution by contacting each oneliter portion thereof with the same volume of the extractant in fivesuccessive stages at a temperature of 50C. Hydrochloric acid removedfrom the solution during extraction of the phosphoric acid was replacedafter each stage of the extraction process by contacting the aqueousphase thereof with 50 milliliters of concentrated aqueous (37 percent)hydrochloric acid.

The aqueous phases of the solution were then combined to produce 1 1.5liters of uranium-containing brine solution. The brine solution wasfound to contain percent of the uranium present in the startingmaterial.

EXAMPLE 2 An acidulation tower equipped with a mechanical stirrer wascharged with a water based slurry of ground Florida phosphate rockcontaining 235 parts uranium (essentially in the hexavalent form) permillion parts of phosphate rock. The slurry was contacted with a streamof hydrochloric acid vapor moving in a direction countercurrent to thatof the slurry. The acidinsoluble residue was removed by settling andfiltration. An acidulate solution was thereby formed which contained26.7 percent calcium chloride, 13.1 percent phosphoric acid, 1.8 percenthydrochloric acid, 0.8 percent ferric chloride, 0.7 percent aluminumchloride, 0.8 percent fluorine and 66 parts uranium (essentially in thehexavalent form) per million parts of solution. These constituents wereheated with vigorous stirring to a temperature of 80C. The stirring wascontinued, the temperature was maintained at 80C and hydrogen sulfidewas directed through the acidulate solution until the electromotivepotential developed between platinum and saturated calomel electrodesimmersed therein decreased from an initial value of +0.52 volt to fromabout +0.15 to 0.20 volt. When the latter voltage was developed betweenthe electrodes, substantially all of the iron and uranium present in thesolution had been converted to the divalent and tetravalent states,respectively.

The reduced acidulate solution was divided into ten one-liter portions.An extractant was prepared by saturating a mixture of 80 percentisobutanol and 20 percent n-heptane with water at 50C. Substantially allof the phosphoric acid was extracted from the acidulate solution bycontacting each one-liter portion thereof with the same volume of theextractant in five successive stages at a temperature of 50C.Hydrochloric acid removed from the solution during extraction of thephosphoric acid was replaced after each stage of the extraction processby contacting the aqueous phase thereof with 50 milliliters ofconcentrated aqueous (37 percent) hydrochloric acid.

The aqueous phases were then combined to produce 1 1.5 liters of a brinesolution containing 24.1 percent calcium chloride, 0.1 percentphosphoric acid, 2.0 percent hydrochloric acid, 0.6 percent ferrouschloride, 0.6 percent aluminum chloride, 0.7 percent fluorine and 50parts uranium per million parts of solution. As indicated by thecomposition of the brine solution, more than 99 percent of thephosphoric acid was extracted from the acidulate solution, while thebrine solution contained substantially all of the calcium chloride,aluminum chloride, and fluorine, 84 percent of the uranium and percentof the iron thereof. Moreover, the uranium and iron contained by thebrine solution was reduced to the tetravalent and divalent states,respectively.

The brine solution was then transferred to an oxidizing vessel whereinit was brought into contact with a 30 percent aqueous solution of sodiumchlorate. Contact between the sodium chlorate and the aqueous phase ofthe solution was continued at a temperature of 50C. until theelectromotive potential developed between the platinum and saturatedcalomel electrodes immersed therein increased for an initial value of+0.20 volt to a value of +0.30 volt. When the latter voltage wasdeveloped between the electrodes, substantially all of the uraniumpresent in the solution had been converted to the hexavalent state. As aprecautionary measure, the solution was then brought into contact with 2liters of sulphur dioxide gas for each gram of sodium chlorate employedto ensure that substantially all of the iron remained in the divalentstate during oxidation of the uranium to the hexavalent state.

The latter solution was fed to an ion exchange vessel having a 20millimeter column of 50-100 American Standard Mesh Dowex-l-X4 anionexchange resin in chloride form. Passage of the solution through thecolumn was continued at a temperature of 50C. and at a flow rate of 5milliliters per minute until the uranium concentration in the effluentfrom the column increasedto about that of the feed solution. The columnwas scrubbed with 40 milliliters of a 7 molar hydrochlo-.

ric acid solution, passed therethrough at a flow rate of 10 millilitersper minute. Seventy milliliters of water were then passed through thecolumn at a flow rate of 3 milliliters per minute to strip the uraniumfrom the column. An aqueous solution of uranyl chloride resulted whichcontained 520 milligrams of uranium in each 70 milliliters of solution.

To the resulting solution were added 0.19 gram of 100 percent hydrogenfluoride, 0.89 gram of ammonium fluoride, 0.32 gram of hydroxylamineacid sulfate, a trace of copper sulfate (CuSO and one drop of 37%concentrated hydrochloric acid (as a catalyst). The solution was thenboiled for minutes during which time 90% of the uranium containedtherein pre' cipitated in the form of ammonium uranous pentafluoride.

The ammonium uranous pentafiuoride was filtered from the solution,washed and then calcined at 350C. After a few minutes substantially allof the ammonium fluoride was volatilized and pure uranium tetrafluoridewas obtained.

EXAMPLE 3 An 11.5 liter uranium-containing brine solution was preparedfrom 10 liters of an acidulate solution containing 26.7 percent calciumchloride, 13.1 percent phosphoric acid, 1.8 percent hydrochloric acid,0.8

- percent ferric chloride, 0.7 percent aluminum chloride,

0.8 percent fluorine and 66 parts uranium (essentially in the hexavalentform) per million parts of solution by the solvent extraction process ofExample 2. A first portion of the uranium-containing brine solutionhaving a volume of 0.5 liter was heated to C. The temand trivalentstates, respectively. After being oxidized,

the first portion of the uranium-containing brine solution, containingall of its iron in the form of ferric chloride, was added to theremaining 11.0 liters (second portion) of the solution at 50C. wherebyall of the uranium of the second portion was oxidized to the hexavalentstate according to the formula 2FeCl U (IV) ZFeCl U (VI) 2Cl'.

The first and second portions thus combined were processed in the mannerdescribed in Example 2. The uranium tetrafluoride recovered representedmore than of the uranium present in the acidulate solution.

Having thus described the invention in rather full detail it will beunderstood that these details need not be strictly adhered to but thatvarious changes and modifications may suggest themselves to one skilledin the art, all falling within the scope of the invention as defined bythe subjoined claims.

What is claimed is:

l. A process for recovering uranium from a solution containingphosphoric acid, uranium in the hexavalent state and a chloride saltselected from the group consisting of alkali metal chloride, alkalineearth metal chloride and ammonium chloride, comprising the steps of:

a. contacting the solution with a reductant capable of converting saiduranium from the hexavalent to the tetravalent state;

b. contacting said reduced solution with an organic extractant capableof separating said phosphoric acid from the reduced solution and leavingsaid tetravalent uranium in said reduced solution; and

c. recovering said tetravalent uranium from said reduced solution.

2. A process as recited in claim 1 wherein said solution is obtained byhydrochloric acid digestion of phosphate rock.

3. A process as recited in claim 1 wherein said uranium is recoveredfrom said remaining constituents of said solution by:

a. contacting said remaining constituents with an oxidant capable ofconverting said uranium from the tetravalent to the hexavalent state;

b. contacting the oxidized solution with an anion exchange resin capableof adsorbing said uranium;

c. removing said uranium from said anion exchange resin by means of asolvent; and

d. recovering said uranium from the resulting solution.

4. A process as recited in claim 1 wherein said reductant is selectedfrom the group consisting of elementary iron, elementary aluminum,hydrogen sulfide, sodium hydrosulfite and formaldehydesodiumhydrosulfoxylate.

5. A process as recited in claim 1 wherein the reduction step is carriedout at a temperature ranging from about 10C. to the boiling point ofsaid solution.

6. A process as recited in claim 1 wherein the extractant is selectedfrom the group consisting of butanols, pentanols, trialkylphosphateshaving alkyl groups containing from 2 to 8 carbon atoms,N,N-disubstituted amides derived from monocarboxylic acids having 1 to 3carbon atoms, and mixtures thereof with each other and withhydrocarbons.

7. A process as recited in claim 3 wherein the oxidant is selected fromthe group consisting of trivalent iron salts, sodium chlorate, sodiumhypochlorite, sodium chlorite and elementary chlorine.

8. A process as recited in claim 3 wherein the oxidation step is carriedout at a temperature ranging from about C. to the boiling point of thesolution.

9. A process as recited in claim 3 wherein said oxidized solution is a 3to [0 molar chloride ion solution.

10. A process as recited in claim 3 wherein said uranium is recoveredfrom the solution of step d by:

a. neutralizing said solution;

b. contacting said solution with a sufficient quantity of ammonia toprecipitate a hexavalent uraniumcontaining compound therefrom; and

c. washing and calcining said compound to produce uranium trioxide.

11. A process as recited in claim 3 wherein said urato form uraniumtetrafluoride.

1. A PROCESS FOR RECOVERING URANIUM FROM A SOLUTION CONTAININGPHOSPHORIC ACID, URANIUM IN THE HEXAVALENT STATE AND A CHLORIDE SALTSELECTED FROM THE GROUP CONSISTING OF ALKALI METAL CHLORIDE, ALKALINEEARTH METAL CHLORIDE AND AMMONIUM CHLORIDE, COMPRISING THE STEPS OF: A.CONTACTING THE SOLUTION WITH A REDUCTANT CAPABLE OF CONVERTING SAIDURANIUM FROM THE HEXAVALENT TO THE TETRAVALENT STATE; B. CONTACTING SAIDREDUCED SOLUTION WITH AN ORGANIC EXTRACTANT CAPABLE OF SEPARATING SAIDPHOSPHORIC ACID FROM THE REDUCED SOLUTION AND LEAVING SAID TETRAVALENTURANIUM IN SAID REDUCED SOLUTION; AND C. RECOVERING SAID TREAVALENTURANIUM FROM SAID REDUCED SOLUTION.
 2. A process as recited in claim 1wherein said solution is obtained by hydrochloric acid digestion ofphosphate rock.
 3. A process as recited in claim 1 wherein said uraniumis recovered from said remaining constituents of said solution by: a.contacting said remaining constituents with an oxidant capable ofconverting said uranium from the tetravalent to the hexavalent state; b.contacting the oxidized solution with an anion exchange resin capable ofadsorbing said uranium; c. removing said uranium from said anionexchange resin by means of a solvent; and d. recovering said uraniumfrom the resulting solution.
 4. A process as recited in claim 1 whereinsaid reductant is selected from the group consisting of elementary iron,elementary aluminum, hydrogen sulfide, sodium hydrosulfite andformaldehydesodium hydrosulfoxylate.
 5. A process as recited in claim 1wherein the reduction step is carrieD out at a temperature ranging fromabout 10*C. to the boiling point of said solution.
 6. A process asrecited in claim 1 wherein the extractant is selected from the groupconsisting of butanols, pentanols, trialkylphosphates having alkylgroups containing from 2 to 8 carbon atoms, N,N-disubstituted amidesderived from monocarboxylic acids having 1 to 3 carbon atoms, andmixtures thereof with each other and with hydrocarbons.
 7. A process asrecited in claim 3 wherein the oxidant is selected from the groupconsisting of trivalent iron salts, sodium chlorate, sodiumhypochlorite, sodium chlorite and elementary chlorine.
 8. A process asrecited in claim 3 wherein the oxidation step is carried out at atemperature ranging from about 10*C. to the boiling point of thesolution.
 9. A process as recited in claim 3 wherein said oxidizedsolution is a 3 to 10 molar chloride ion solution.
 10. A process asrecited in claim 3 wherein said uranium is recovered from the solutionof step d by: a. neutralizing said solution; b. contacting said solutionwith a sufficient quantity of ammonia to precipitate a hexavalenturanium-containing compound therefrom; and c. washing and calcining saidcompound to produce uranium trioxide.
 11. A process as recited in claim3 wherein said uranium is recovered from the solution of step d by: a.evaporating said solution so as to bring the uranium concentrationthereof to at least about 1 percent by weight of the solution; b.contacting said solution with a sufficient amount of a reductant toreduce the uranium therein from the hexavalent to the tetravalent state;c. contacting the reduced solution with a sufficient amount of hydrogenfluoride and ammonium fluoride to precipitate the uranium from saidsolution in the form of crystalline ammonium uranous pentafluoride; andd. separating, washing and calcining the precipitate to form uraniumtetrafluoride.